I'm busy prototyping an alarm clock. It's going to have a loud alarm (12v), and I need the alarm to work even when there's no power from the outlet. I'd like some recommendations on what batteries would be best to use, I probably only need it to be activated for 5-10 min while running on batteries.
Also, can I change the volume of the alarm by adding or removing resistors?
Please post a data sheet or a link to a discription of the 12V alarm
Nicad are easy (no complicated charging circuit) to use. no fire hazard and not expensive.
Thanks @gilshultz. Should I be using 18650 3.3v or just plain 1.5v rechargeable batteries? I'd like the batteries to charge while power is connected. If I use 3.3v batteries, should I use 4 of them which will be 13.2v?
Yes, but lithium-based batteries require special charging circuitry, and to charge them in series requires charge balancing circuitry.
A sealed lead-acid gel cell can be float charged indefinitely, without special circuitry. Likewise for a 10xAA NiMH battery pack.
See batteryuniversity.com for the details.
Thanks jremington. If I use NiMH, will I just need a transformer to convert power source to 12V? For Lithium batteries, would I need additional circuitry? Which circuitry?
The sealed lead acid batteries are pretty large and heavy. Using 10 AA batteries is an option but would work out quite expensive. Do you know of any 12v NiMH batteries that are quite small?
Your horn uses 12V @ 30A
I don't think that any of the batteries that @jremington suggested could supply that much current.
@jremington any other suggestions?
You'd need something like a car battery and 150dB can make you deaf! (The actual dB SPL level depends on how far you are from the noise source.)
...The spec is probably exaggerated but it still could be dangerously/annoying loud if you are too close or in an enclosed room,
No.
Thanks for that feedback. I decided to use a less loud buzzer (see screenshot) that requires less current
Thanks @jremington . If I did decide to use the 18650s instead, could I use a battery management system like the screenshot shown?
If you decide to try it, let us know if it works satisfactorily.
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